1. Field of the Invention
The present invention is directed to methods and devices for dispersion of high solids toner, and in particular to methods and devices of this type which are capable of dispersing high solids toner having toner particle concentration of 40% and higher solids by weight into a working developer solution for use in an image forming devices such as an electrostatic copying machines.
2. Discussion of the Related Art
In electrostatic copying machine, a photosensitive drum is in contact with liquid developer comprising a toner carrier liquid with toner particles dispersed therein. The toner particles of the working developer solution are electrostatically attracted to an electrostatic latent image on the drum. In electrostatic copy machines, a working developer solution having 1%-2% solids by weight of toner particles is used to develop the latent image into a visible toner image.
As the latent image is developed into a visible toner image, the amount of toner particles in the working developer solution is depleted. A replenishing system coupled to the developer tank replenishes the depleted toner particles in the working developer solution. A concentrated developer solution having a toner particle concentration of approximately 10% to 20% solids by weight is usually used to replenish the toner particle depleted working developer solution.
However, the toner particles in the developer solution are depleted more rapidly when successively producing many copies or when copying an original with a large solid image area such as color originals which often have inked areas covering over 40% of the original. Since the proportion of toner carrier liquid (80% to 90%) is much larger than that of the toner particles (10% to 20%) in the concentrated developer solution, the total amount of toner carrier liquid in the working developer solution is increased. For example, if 10% toner particle solution (90% Isopar.RTM.) is used for replenishment, Isopar.RTM. will rapidly build up in the machine. Further, continuous supply of concentrated developer solution to the developer tank can result in an overflow of the toner carrier liquid in the developer tank.
As environmental restrictions to the release of carrier liquid such as Isopar.RTM. to the atmosphere increase, it is important to recover and recirculate the carrier liquid in the developer tank. This requirement makes it even more difficult to maintain the proper mixture ratio without overflowing the developer tank. While level sensors can be used to shut off the replenishment to prevent the overflow situation, copiers copying large area color originals, however, quickly achieve the preset level and are forced to shut down.
Another method of replenishing the toner is the batch process, in which a batch of developer solution having 10% toner particle concentration is prepared in two separate chambers. When the concentration of toner particles falls below 2%, the first chamber gradually releases the batch of developer solution into the developer solution until its supply of batch solution is depleted. Thereafter, the second chamber releases the batch of developer solution whenever the concentration of toner particles falls below 2%. While the second chamber is depleting its supply of the batch solution, the first chamber is replenished with another batch of developer solution. When the second chamber depletes its supply, the process used for the first chamber is repeated for the second chamber. The batch process is disadvantageous because: 1) the preparation of the batch of developer solution is time consuming; and 2) the use of two chambers, rather than one chamber, is not cost efficient.
Another solution is to replenish the developer with replenisher liquid developer having toner particle concentration of 17%-55% by weight. In U.S. Pat. No. 4,860,050 to Kurotori et al., a developing replenisher material or a replenisher liquid developer is supplied to a developer tank of a copy machine. The toner particles of the replenisher liquid developer may be fed into a discharge member contained in a separate chamber. Spiral rollers break the toner particles into smaller toner particles. Further, the discharge member immersed in the liquid developer may have a plurality of small outlet ports and a pair of rotatable spiral rollers having a spiral vane or fin around its peripheral surface. The spiral rollers have axes extending longitudinally of the discharge member and pulley ends around which a drive belt is trained. In another embodiment of Kurotori et al., a jet flow from a pipe forces any replenisher liquid developer which is not well dispersed against a mesh body for dispersion into the liquid developer.
In U.S. Pat. No. 4,794,066, Taggi et al. disclose a process for preparing a liquid developer comprising the steps of: (1) mixing intimately a water-wet presscake pigment with at least one water insoluble vehicle; (2) removing all the water; (3) dispersing at an elevated temperature in the vehicle under high shear the pigment dispersion, a thermoplastic resin, and a non-polar liquid, wherein a temperature is being maintained to plasticize and liquify the resin; and (4) cooling the dispersion. A toner concentrate comprising Isopar may pass through a mesh sieve.
Neither of the two U.S. patents discloses methods and devices for adding toner particles and carrier liquid to the developer tank at a rate equivalent to the consumption rate and to prevent the overflow of the carrier liquid in the developer tank. Further, neither of the two U.S. patents discloses methods and devices using high shear forces to disperse high solids toner in a working developer solution.
All references cited in the specification, and their references, are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features, and/or technical background.